General
These are the components that have a digital interface with the multi-mode receivers:
Captain and first officer NAV control panels
Flight data acquisition unit (FDAU)
Standby attitude indicator
Ground proximity warning computer (GPWC)
Flight management computer (FMC) 1 and 2
Display electronics units (DEU)
FCC A and FCC B.
Digital Inputs
The NAV control panels supply frequency tune inputs to the multi-mode receivers. The NAV control panels also send tune inputs to the VOR and DME systems on a separate data bus.
Digital Outputs
Each MMR has two output data buses. Output data bus 1 goes to the FCCs. Output data bus 2 goes to many components. The FDAU receives ILS data and status of the MMR receivers.
The FDAU processes the data for the flight data recorder.
The standby attitude indicator uses localizer and glideslope deviations for the ILS deviation bar operation. Only MMR 1 sends ILS data to the standby attitude indicator.
The GPWC receives glideslope data from both ILS receivers for mode 5 (below glideslope) warnings.
FMC 1 and FMC 2 receive ILS data and receiver status from the two MMRs. The FMCS uses the ILS data for position update calculations.
The FCCs use ILS data to calculate airplane steering
commands for the digital flight control system (DFCS)
autopilot and flight director modes.
The DEU 1 receives two inputs from MMR 1 and two inputs from MMR 2. DEU 2 also receives two inputs from MMR 1 and two inputs from MMR 2. The CDS uses the ILS data to calculate the localizer deviation and glideslope deviation displays.
ILS - FREQUENCY TRANSFER AND INSTRUMENT SWITCHING
General
The frequency transfer switch on the NAV control panel and the VHF NAV transfer switch on the navigation/displays source select panel have interface with the FCCs and DEUs.
Frequency Transfer Switch
The frequency transfer switch on the NAV control panel permits the crew to transfer the frequency from the standby display window on the NAV control panel, to the active display window. The transfer switch is a momentary action switch. When you push the switch, it changes the discrete level to the FCCs. The discrete tells the FCC when there is an ILS frequency change.
Navigation/Displays Source Select Panel
The VHF NAV switch on the navigation/displays source select panel is a three position switch. The positions are; BOTH ON 1, NORMAL, and BOTH ON 2. This switch changes the source of the data that the DEUs use for the ILS displays.
In the NORMAL position, MMR 1 supplies data for the captain displays and MMR 2 supplies data for the first officer displays. When you select BOTH ON 1, the DEUs use MMR 1 as the source for the captains displays and first officers displays.
When you select BOTH ON 2, MMR 2 is the source for the captains displays and first officers displays.
Discrete signals also go to the flight control computers (FCCs) to signal that the switch is not in the normal position.
ILS - ANTENNA INTERFACE
General
The multi-mode receivers (MMRs) get RF inputs from these antennas:
VOR/LOC antenna on the vertical stabilizer
Localizer antenna in the nose radome
Glideslope antenna in the nose radome.
The VOR/LOC antenna RF inputs go through the power dividers then to the localizer (LOC) antenna (ANT) switches.
The localizer antenna RF inputs go directly to the LOC ANT switches. The antenna switches select the VOR/LOC antenna or localizer antenna as the source of the localizer RF signal input to the MMRs.
The glideslope antenna inputs do not go through the antenna switches. Glideslope antenna RF inputs go directly to the MMRs.
When you tune an ILS frequency on the navigation (NAV) control panels, they send 28v dc to the LOC antenna switches. The LOC ANT switches use 28v dc from the NAV control panels and a discrete signal from the integrated flight system accessory unit (IFSAU) for operation.
The IFSAU sends the discrete when it receives a discrete from the Flight Control Computers (FCCs). The FCCs send the discrete when you select the approach (APP) or localizer (LOC) mode on the DFCS mode control panel.
ILS - ANALOG INTERFACES